[R-390] R-390A balanced input question
Larry H
dinlarh at att.net
Mon Sep 22 20:04:21 EDT 2014
Hi Jim, One of the problems we can have on R390-A's is bad connections in the tuned circuits on the rf deck. All the rectangular cans with variable core tuning are 'plug in's held in by 1 phillips screw under the moving core. The contacts can get oxidized or corroded and is usually easily fixed with deoxit. And, sometimes, unfortunately, the antenna coils get cooked by close tx power when antenna is still connected to rx. The rf cans are easy to take apart and look inside once removed. And then there's the band switch problem. I had 1 of those recently - yuk! I wish you good luck with it.
Very sorry to hear about you mother-in-law.
Regards, Larry
On Monday, September 22, 2014 10:46 AM, JAMES GREEN <jagreen3 at sbcglobal.net> wrote:
Thanks to all of you that responded!
I have learned a lot from you. I have several sig gens in the shop and will look into this when I get a chance. This oportunity is WAAAAAY out there. I'm currently the main support advocate for my Mother-In Law who is in the local Hospice program. I am writing this from a certesy PC athe the UW hospital.
I pulled out my old R-392 and have that up and running now. I haven been able to give much quality time yet so I havent found the BBC out of ascention island yet.
Thanks again!
Jim
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Today's Topics:
1. Re: R-390A balanced input question (Craig Heaton)
2. Re: R-390A balanced input question (Larry H)
3. Re: Balance Caps (Steve Hobensack)
4. Poor Man's J104 Balanced antenna connector (Craig Heaton)
5. Re: Poor Man's J104 Balanced antenna connector (Larry H)
----------------------------------------------------------------------
Message: 1
Date: Sun, 21 Sep 2014 19:22:25 -0700
From: "Craig Heaton" <hamfish at efn.org>
To: <r-390 at mailman.qth.net>
Subject: Re: [R-390] R-390A balanced input question
Message-ID: <000001cfd60c$0d81b670$28852350$@org>
Content-Type: text/plain; charset="us-ascii"
Sorry Jim, we most likely took off on a tangent. So, do you have a sig-gen?
If so, connect it to the balanced input and trace the signal thru the
receiver with a scope. Swap the coax between the balanced & unbalanced, what
happens then?
The balanced signal has to pass thru a couple more switch contacts, dirty?
Craig,
-----Original Message-----
From: R-390 [mailto:r-390-bounces at mailman.qth.net] On Behalf Of JAMES GREEN
Sent: Sunday, September 21, 2014 9:40 AM
To: r-390 at mailman.qth.net
Subject: [R-390] R-390A balanced input question
I have way too many projects to work on and just want to have a good
receiver to listen to when I'm not in the shop. I have an EAC R-390A that I
used to listen to quite regularly about a year ago. I put it aside for a few
months and started listening more to 2 channel Hi-Fi. I had the yen to catch
the BBC out of ascension Island again so I pulled it out and ran into a
small problem.
Knew exactly where the radio was stored. I can't for the life of me find the
"C" to so-239 adapter I used before to hook it to my antenna. I did find a
balanced to SO-239 adapter, but I found I could not get a signal from the
balanced input. Upon close inspection and some dis-assembly I found the
plastic insert in the balanced connector was twisted. This twisted the relay
contacts so there was no connection. I replaced the antenna relay with one
from my parts radio & have verified it is now passing a signal.
Here is the problem:
I still am unable to pick up anything through the balanced input. Upon
looking in the R-390A Y2K manual schematics it looks like the unbalanced
connector bypasses several tuned transformers that the unbalanced input does
not bypass. I suspect these tuned transformers are in need of alignment.
However, the alignment procedure in the Y2K manual instructs one to connect
the sig gen to the unbalanced connector. & aligning from there.
Am I missing something? Is there a separate alignment procedure that I did
not find that shows how to align from the balanced input?
Cash flow at the moment prevents buying another "C" to SO-239 adapter, & I
have heard some extra sensitivity can be gained by using the balanced input.
Jim
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Message: 2
Date: Sun, 21 Sep 2014 19:53:27 -0700
From: Larry H <dinlarh at att.net>
To: '390 list' <r-390 at mailman.qth.net>
Subject: Re: [R-390] R-390A balanced input question
Message-ID:
<1411354407.31493.YahooMailNeo at web181601.mail.ne1.yahoo.com>
Content-Type: text/plain; charset=us-ascii
Hi Jim and Craig, Sorry, I got your names reversed on my previous post.
To all - It's important to note that the impedance on the C connector (J103) originally connected to P205, which is the hi impedance input is about 1 meg ohm. This connection was designed to connect a whip antenna to it through a very short piece of coax. The whip became part of the tuned circuit input to the rf amp and did not diminish the effectiveness of the secondary of T201-T206. This allowed the Q of the antenna circuit to reduce unwanted images, adjacent stations and noise from entering the rf amp as much as possible for a whip antenna. This also reduces IMD produced in the rf amp. However, by connecting a low impedance antenna to this connection, the Q is severely reduced and the benefits of the tuned circuit are greatly removed. If you want to take advantage of the filtering available in the antenna circuit for a low impedance antenna (ie any coax of some length (more than 20' from rx to antenna)) it's better to use the balanced input.
This can be done as explained elsewhere. The impedance on rx's is not near as critical as tx's, so the small mismatch is not an issue. The design of the R390-A's balanced input is good for impedances of 50 to 200 ohms. Using an rf xformer to match it to 50 ohm coax is not productive. I've tried many and the insertion loss is =/> a direct coax connection on very weak signals.
Where the impedance matching is important is when you are measuring signal to noise ratio using the balanced input. Otherwise, it's not important to be right on.
Regards, Larry
On Sunday, September 21, 2014 5:12 PM, Craig Heaton <hamfish at efn.org> wrote:
Just an observation of someone that didn't have radio as an occupation.
As Charles noted, an antenna tuner/matchbox is an exception to matching a
resonate antenna to 50 ohms. On my two stations using a tuner, the VSWR is
flat 1 to 1, and the antenna trim control is at 0 for max indication on the
carrier level meter. This is an indication peaking the RF section with
regard as to antenna type/plus tuner during RF alignment has advantages.
Now, changing nothing but the KC knob, moving up or down in frequency, the
antenna trim will have to be tweaked to bring the carrier level back to a
peak. In my present use of a R-390/A paired with a transmitter, I'll take
the advantage of using the balanced antenna input & tuned primaries of
T201-T206. The antenna trim control will make up for things not quite at
optimum impedance at the antenna input.
YMMV
Craig
-----Original Message-----
From: R-390 [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Charles
Steinmetz
Sent: Sunday, September 21, 2014 4:11 PM
To: 390 list
Subject: Re: [R-390] R-390A balanced input question
>If you use the balanced input you can go through and trim up the 1st RF
>stages. Make sure you use the same hook-up that you are going to run with.
> * * *
>If you use a balun (2.25:1 or 2:5:1) then you need to do the alignment
>through that connection. Make sure you set the ANT-TRIM knob to the center
> * * *
>You are peaking performance. Usually I shoot for the middle of the band
>that is associated with that RF stage. Since I use one of the
>German-made baluns I do the alignment from a 50 ohm unbalanced
>connection from my signal generator
That's all well and good, but there are only a few, very narrow frequency
ranges between 500kHz and 32MHz at which the receiving antenna will be
anywhere near 50 ohms. So in the end, anything you can do with a 50 ohm
generator isn't going to be very helpful because using a 50 ohm generator
violates the first principle above, "Make sure you use the same hook-up that
you are going to run with."
Instead, people with random antennas should ignore the balanced input, feed
the unbalanced input, and ignore all the whining they've seen here and
elsewhere about the unbalanced input "bypassing important tuned circuits."
All you're missing are the tuned primaries of T201-206 (depending on the
band selected), and if you aren't matched to them (and the paragraph above
explains why you won't be), you're much better off without them. As a side
benefit, the front end noise of the radio will usually drop significantly
(how much depends on your particular antenna).
The only exception would be if you use an antenna tuner ("matchbox") to
match a resonant antenna to 50 ohms, or if you cut an antenna specifically
to be 50 ohms at some important frequency -- but this can only be true for
very narrow frequency bands, because antenna resonances are very narrow.
Best regards,
Charles
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------------------------------
Message: 3
Date: Mon, 22 Sep 2014 07:43:15 -0400
From: Steve Hobensack <stevehobensack at hotmail.com>
To: r390 reflector <r-390 at mailman.qth.net>
Subject: Re: [R-390] Balance Caps
Message-ID: <BLU172-W52B1888742C8A33BD0467ACAB30 at phx.gbl>
Content-Type: text/plain; charset="iso-8859-1"
I adjusted for a dip at the junction of two 100 ohm resistors (200 ohms balanced). That way, it is balanced for my ham band 50 ohm antenna through a simple 4 to 1 balun.
Steve N8YE
> Message: 4
> Date: Sun, 21 Sep 2014 16:51:37 -0700
> From: "Craig Heaton" <hamfish at efn.org>
> To: <r-390 at mailman.qth.net>
> Subject: [R-390] Balance Caps
> Message-ID: <000001cfd5f6$fcaf1f00$f60d5d00$@org>
> Content-Type: text/plain; charset="us-ascii"
>
> To All:
>
> For what it is worth, something I printed from Chuck's website years ago.
> Hope Chuck doesn't mind.
>
> Balance Caps
>
> Note: It is my opinion that this is an important step which is often
> overlooked. You're basically nulling out any signals that are not balanced.
> Some noise is of this type. This adjustment can make the receiver quieter in
> the presence of common-mode noise.
>
> Connect the signal generator to the junction of two 68 ohm resistors.
*******************
------------------------------
Message: 4
Date: Mon, 22 Sep 2014 05:24:15 -0700
From: "Craig Heaton" <hamfish at efn.org>
To: <r-390 at mailman.qth.net>
Subject: [R-390] Poor Man's J104 Balanced antenna connector
Message-ID: <000601cfd660$210d2db0$63278910$@org>
Content-Type: text/plain; charset="us-ascii"
After the first R-390/A followed me home, connecting a sig-gen or antenna
became an issue. Thank goodness for the web. Chuck Rippel's (sp?) website
had a good solution. A homemade bracket, SO-239 connector, a little wire,
etc; and a person could lash-up their favorite PL-259 and get started. I
think someone here on the list has saved Chuck's site and the info is still
available?
A short drive to "The People's Republic of Eugene, OR" takes me to one of
the last mom & pop electronic stores left. Here I found a cheap temporary
solution, twinax connectors. Mom & Pop put a price on them years ago and
never raised the price per inflation, etc. Those little pins in the twinax
connector fit J104 perfect.
On the cheap, solder one pin to the center conductor of RG58. With the
braided shield fit as many strands as possible into the other pin & solder.
The rest of the shield/braid is soldered to a small spade lug. Center
conductor goes to the right hand side of J104, pin with braid to the other
side of J104, lug to Phillips screw under J104. The other end of the RG58
can go to antenna, TX/RX relay, etc.
Since the price was right at the time, I made one up with just a short
length of RG58 with a female BNC connector, used at the time for the lash-up
to a sig-gen.
Better than nothing? On the cheap is not sturdy, bend the center conductor &
pin several times, it will break. The gasoline to Mom & Pop's store was more
than the twinax connectors. YMMV
Craig,
------------------------------
Message: 5
Date: Mon, 22 Sep 2014 09:52:09 -0700
From: Larry H <dinlarh at att.net>
To: "r-390 at mailman.qth.net" <r-390 at mailman.qth.net>
Subject: Re: [R-390] Poor Man's J104 Balanced antenna connector
Message-ID:
<1411404729.72005.YahooMailNeo at web181605.mail.ne1.yahoo.com>
Content-Type: text/plain; charset=us-ascii
The male Amphenol twinax connector 82-5589-rfx that matches the balanced J104 connector on R390-A's is available on ebay for $4.25 + $2.25 shipping.
Regards, Larry
On Monday, September 22, 2014 5:24 AM, Craig Heaton <hamfish at efn.org> wrote:
After the first R-390/A followed me home, connecting a sig-gen or antenna
became an issue. Thank goodness for the web. Chuck Rippel's (sp?) website
had a good solution. A homemade bracket, SO-239 connector, a little wire,
etc; and a person could lash-up their favorite PL-259 and get started. I
think someone here on the list has saved Chuck's site and the info is still
available?
A short drive to "The People's Republic of Eugene, OR" takes me to one of
the last mom & pop electronic stores left. Here I found a cheap temporary
solution, twinax connectors. Mom & Pop put a price on them years ago and
never raised the price per inflation, etc. Those little pins in the twinax
connector fit J104 perfect.
On the cheap, solder one pin to the center conductor of RG58. With the
braided shield fit as many strands as possible into the other pin & solder.
The rest of the shield/braid is soldered to a small spade lug. Center
conductor goes to the right hand side of J104, pin with braid to the other
side of J104, lug to Phillips screw under J104. The other end of the RG58
can go to antenna, TX/RX relay, etc.
Since the price was right at the time, I made one up with just a short
length of RG58 with a female BNC connector, used at the time for the lash-up
to a sig-gen.
Better than nothing? On the cheap is not sturdy, bend the center conductor &
pin several times, it will break. The gasoline to Mom & Pop's store was more
than the twinax connectors. YMMV
Craig,
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